In recent years, the use of a user terminal including a cellular communication unit and a WLAN communication unit (a so-called dual terminal) is widely spread. Furthermore, the number of WLAN access points (hereinafter briefly referred to as an “access point”) managed by an operator of a cellular communication scheme increases.
To respond to this situation, ANDSF (Access Network Discovery and Selection Function) is being standardized to make efficient an access point discovery process by a user terminal.
Further, in 3GPP (3rd Generation Partnership Project) which is a project aiming to standardize a cellular communication system, it is planned to study a technology enabling strengthening of cooperation in wireless access network (RAN) level between a cellular communication system and a WLAN system (see Non Patent Document 1).
One of the objects of such a technology is to establish a good balance at a load level between a cellular base station and an access point by improving the usage of an access point.
In the ANDSF, an ANDSF server arranged in a core network provides a user terminal with information on WLAN by way of a NAS (Non Access Stratum) message. The user terminal selects the cellular base stations and the access points on the basis of the information provided from the ANDSF server to establish a balance at a load level.
Further, the user terminal is notified of a RAN rule set in a cellular RAN. The RAN rule is used to establish a load balance between the cellular base station and the access point in response to an actual load situation, etc., of the cellular base station.